A conventional connection structure of this kind for a branching connector is shown in FIG. 7, where a main tube 11 acts as a fuel rail provided with a channel 11'. A hole 11" extends through the wall around the main tube 11, and is in communication with the channel 11' in the main tube. The hole 11" is of simple circular cross section. A branch tube 12 acting as a branching connector is inserted in the hole 11". The branch tube 12 has a connection end 12' which is neither enlarged nor shrunk. Under this condition, the connection end 12' is brazed at 13 to the main tube, thus forming a connection structure.
In this connection structure built by the prior art technique, fluid under high pressure amounting to 1000 kgf/cm.sup.2 or more is constantly and repeatedly supplied. The pressure is rapidly changed. Vibrations are given especially from the engine. The ambient temperature is elevated and lowered, causing the relative dimensions of the opposite members (the opposite seat surfaces) to vary. Especially, where the diameter of the branching connector is small compared with the diameter of the main tube 11, when the main tube is brazed to the branching connector, local heating deteriorates the mechanical strength near the brazed portion 13. As the tubes get fatigued due to vibrations, cracks are easily produced. As a result, leakage of the fuel may occur frequently.
In view of the foregoing problems with the prior art technique, the present invention has been made. It is an object of the invention to provide a connection structure for a branching connector used in a high-pressure fuel rail, the connection structure having a connected portion in which two components are brazed together firmly. The connection structure is further characterized in that stress in the branching connector near the connected portion due to fatigue is effectively dispersed. If the connection structure is placed in position and repeatedly supplied with fluid under high pressure which varies rapidly, or if the relative dimensions are varied by the variations in the pressure of the supplied fluid, application of vibrations, or temperature variations, cracks are effectively prevented from being produced in the branching connector near the connected portion. This eliminates the possibility of leakage of the fuel.